The present invention relates to improvements in gas turbine engines and, more particularly, to an improved fastener for use in high temperature, and high vibration environments including a deformable cylinder locknut which lockingly engages a threaded bolt or stud shaft and torsionally seats against a surface by providing for thread-to-thread contact between the nut and bolt over a first undeformed threaded seat portion of the nut, minimal or no contact over a second unthreaded transitional portion of the nut and thread to sleeve contact over a third elliptically deformed unthreaded portion of the nut. In particular, the locknut of the present invention provides a controlled amount of high friction contact between a locknut and a mating bolt.